Build Your Own Faraday Cage. Here’s How.

by Arthur Bradley

Introduction to Faraday Cages

There is a great deal of confusion about Faraday cages. Not only about how to build them, but also what they actually protect against. In this article, Dr. Arthur Bradley, author of Disaster Preparedness for EMP Attacks and Solar Storms, answers a few basic questions and perhaps debunks a few myths.

What is a Faraday Cage?

A Faraday cage (a.k.a. Faraday shield) is a sealed enclosure that has an electrically conductive outer layer. It can be in the shape of a box, cylinder, sphere, or any other closed shape. The enclosure itself can be conductive, or it can be made of a non-conductive material (such as cardboard or wood) and then wrapped in a conductive material (such as aluminum foil).

Faraday Cage box

Faraday Cage Construction

What does it do?

A Faraday cage works by three mechanisms: (1) the conductive layer reflects incoming fields, (2) the conductor absorbs incoming energy, and (3) the cage acts to create opposing fields. All of these work to safeguard the contents from excessive field levels. A Faraday cage is particularly useful for protecting against an electromagnetic pulse that may be the result of a high-altitude nuclear detonation in the atmosphere (a.k.a. EMP attacks).

Despite rumors to the contrary, a Faraday cage is not necessary to protect against solar coronal mass ejections because the frequency content of such disturbances is at much lower frequencies—they don’t couple energy efficiently into small-scale electronics, except through conducted paths (e.g., wires coming into the system). A better precaution against solar events is to unplug electronics and use quality surge suppressors.

How does field cancelation work?

Field cancelation occurs when the free carriers in the conductive material rapidly realign to oppose the incident electric field. If the cage is made from something non-conductive, the free carriers are not mobile enough to realign and cancel the incident field.

How thick should the conducting layer be?

The conductive layer can be very thin because of something known as the skin effect. That term describes the tendency of current to flow primarily on the skin of a conductor. As long as the conducting layer is greater than the skin depth, it will provide excellent shielding because the absorption loss will be large. The skin depth is a function of the frequency of the wave and the conductor material. As an example, consider that for a frequency of 200 MHz, the skin depth of aluminum is only about 21 microns. EMP pulses can have frequency content that ranges up to 1,000 MHz. Therefore, wrapping a box in a couple of layers of heavy duty aluminum foil (typically about 24 microns thick) provides the necessary conductor thickness to protect against high-frequency radiated fields.

Does it matter what type of conductor is used?

Not much. The conductivity of nearly any metal is good enough to allow the carriers to easily realign to cancel external fields. For example, if silver (the best conductor) is used in place of aluminum, the skin depth at 200 MHz is reduced to about 4.5 microns. Of course, the high cost of silver would prevent using it for such a purpose.

Can a Faraday cage have holes?

Yes, as long as the holes are small with respect to the wavelength of the incident electromagnetic wave. For example, a 1 GHz wave has a wavelength of 0.3 meters in free space. As long as the holes are significantly smaller than that dimension (i.e., a few millimeters), they won’t let in much of the incident wave. This is why fine conductive mesh can be used when constructing a Faraday cage. In practice, the cage’s lid or door usually causes the most leakage. Taping the seam with conductive tape helps to reduce this leakage.

Can you use existing conductive enclosures?

Yes, there are many conductive enclosures that can be used, including ammo cans, metal garbage cans, anti-static bags, and even old microwave ovens. Each has its own level of effectiveness as covered in my book, Disaster Preparedness for EMP Attacks and Solar Storms. The key criterion is that the gaps and seams remain very small.

Must the cage be grounded?

There is a great deal of confusion regarding grounding of a Faraday cage. Grounding of the cage (i.e., connecting it to some Earth-referenced source of charge) has little effect on the field levels seen inside the box. Grounding primarily helps to keep the cage from becoming charged and perhaps re-radiating. The bottom line is that an ungrounded cage protects the contents from harmful electromagnetic fields as well as a grounded one.

Anti-static Bags

Anti-static bags are readily available to protect electronic components against electrostatic discharge. They can be purchased in many different sizes, including some large enough to hold radio equipment. While they do offer shielding from EMP, not all products are created equal. Testing confirmed that products certified to MIL-PRF-8170 and/or MIL-PRF-131 offer the greatest protection from an EMP. The results from testing three different types of bags are provided in Disaster Preparedness for EMP Attacks and Solar Storms. When selecting an ESD bag, consider not only the shielding effectiveness but also the physical ruggedness of the bag. A tear or large hole can compromise the bag by allowing EMP energy to enter.

Static Bags

Anti-static Bags

Larger Faraday Cages

Storing a larger set of electronics might require an entire room. Engineers who work in electromagnetics often use “shield rooms” to conduct experiments because they do an excellent job of filtering out interfering signals, providing in excess of 100 dB of shielding. A poor-man’s shield room can be made by lining a small closet with heavy-duty aluminum foil, covering all four walls, the floor, the ceiling, and the inside of the door.

Overlap and tape the seams using either conductive or regular cellophane tape. There can be no conductive penetrations into the room, or it will seriously degrade the shielding. Cover all electrical outlets, light switches, etc. with aluminum foil. Do not plug anything into the electrical outlets. Also, lay a piece of plywood or cardboard on the floor so that it can be walked on without damaging the aluminum foil. Rooms built in this way have been shown to offer more than 50 dB of shielding up to several hundred MHz.

Larger Faraday Cages

For More Information

To buy Dr. Bradley’s EMP book please go to To sign up for his free Practical Prepper Newsletter, Email: [email protected] .

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  1. lilbear68 says:

    youre making faraday cages a complicated mess when for much stuff its very simple. a steel trash can with a tight fitting lid. is all thats needed. just make sure there is no conductive contact to the contents

    • You’re mostly right. A steel trash can with a very tight fitting lid does a pretty good job of acting as a Faraday cage. I tested this as part of my book, and found that it varies greatly depending on the fit of the lid. One addition that helps is to tape the seam of the trash can with conductive tape.

      Stay safe,


      • i have a generator and a few things plugged in to this. if/when i cage the unit, will i still need to do same for plug-ins? (and the ext cords also) if so, sounds like we all ought cage our living spaces!

    • One good test I am told is to put your cell phone inside your makeshift Faraday cage and call it, if you hear ringing from the cell inside, it isn’t properly sealed or thick enough

  2. Does anyone know if you can use packing peanuts to insulate and keep the contents of the cage from contact with the exterior walls?

    • I was told by other pack members that styrofoam makes static electricity.
      Now, the corn starch ones might work. I use chunks of rubber.

      • Styrofoam is an insulator that would work fine in a Faraday cage. The static issue is a concern when two objects are moving with respect to one another (i.e., see the Triboelectric effect). It would be fine sitting inside a Faraday cage as long as you’re not scrubbing your bare electronics against it.

        Stay safe,

  3. Question about gaps: If I use an ammo can with a rubber gasket to make the ammo can (and radio equipment) waterproof, having to repeatedly re-seal the can with conductive tape seems like a real pain. How do I calculate the maximum allowable gap? My first-order thought/guess is that it is related to the frequency spectrum expected in an EMP event.

    • Try lining the lip and lid with steel wool to keep the seal between lid and container.

      • Try to keep the gap smaller than 1 mm (about the thickness of a dime). I tested ammo cans for my book, and they didn’t do great because of the less than perfect seam going around them.


  4. patientmomma says:

    I read on another blog that an old microwave oven (old plugged of course) could be used for small items. Does anyone know if this is true?

    • patientmomma,
      Yes it’s true, and was stated as such in the article.

    • They can, but they are not as effective as other solutions. I did the radio test on mine and found that it failed. I investigated further and found that the FCC currently allows a microwave oven to radiate up to a 1/4 Watt of power and previous standards allowed it to radiate up to 1/2 Watt of power. As such my current 1000 Watt microwave would have 36 dB of shielding. My older 600 Watt microwave would have had only 31 dB of shielding. The author directs you to his book to find the effective shielding of the various recommended containers, but this is at pretty much the lower end of shielding effectiveness.

  5. Thomas T. Tinker says:

    I went for the steel trash can with blanket foam wrap on the inside and a heavy steel wool ‘gasket’ on the lid. 4 harbor freight coffin locks on the lid and a ground server bolt with a leg of jumper cable. I left the clamp on one end to make it ‘portable’. It sits in the basement clamped to the street side of our water meter.

    Whatdayathink ‘Packers’, zit gonna work?

    • TTT,
      I have several 30 gallon metal trashcans setup in a similar manner, except I don’t use any coffin locks, or anything else on the lid since its already tight fitting.
      Also, lose the ground connection. The wire acts as an antenna and unless you have a good way to measure things, my do more harm than good. Faraday enclosures do not have to be grounded, and that is not just my opinion, but the facts from the physics of how they work.
      In general your setup should work fine.

      • From what I read in the article, I’d say don’t loose the ground connection completely. Have it available. The good doctor in his article stated that the faraday cage may become charged itself and having a ground source readily available would be perfect to discharge the cage before you touch it.

  6. bakdrft says:

    I do appreciate the wonderful post people put here, but I do have a question. If I have to store all my electronic items in here how can Iuse them? If I take them out to use how can I put them back in before a EMP is used? Sooo It goes to reason we need to live in a Farady world…or a Faraday car or a…………sigh

    • bakdrft,

      An EMP is not a continuous event, it is a burst of energy that is released, the damage is done, and then it’s gone, unless it is caused by a solar storm which could last for several hours or even days.

      • MD,
        As stated in the article, a solar storm is not likely to produce effects that will hurt small electronic items, unless they are connected to an external long wiring system, which could include the electrical grid, your landline telephone, your local cable TV provider, all of which contain long enough antennas to induce large voltages onto the system, and into connected devices.
        The Carrington Event of 1859 cause problems with telegraph offices because the telegraph wires between the offices acted as a large antenna system, which collected the energy and delivered it to the devices connected to it. Things like spare unconnected batteries stored in those same offices would not have been affected.

    • bakdrft,
      If vulnerable equipment is not in the protected enclosure during the event, then it could be subject to damage. The idea is to store currently unused or spare equipment in the protected environment. I am also one who thinks multiple small enclosures are better than one large enclosure, so that a failure doesn’t damage everything you own. I do the same with my long term food preps, opting to have #10 cans of things like wheat rather than 5 gallon buckets. If the contents of a 5 pound can spoil, it’s a lot less loss than the contents of a 35 pound pail. Likewise for the contents of a single, smaller protective enclosure.

  7. charlie (NC) says:

    The truth is that no one knows for sure what will work without knowing the exact characteristics of electromagnetic pulse and that is impossible to know in advance. I think a metal trash can is as good as anything. I have one lined with heavy cardboard with the seams taped to act as an insulator. However I expected that it would shield
    radio waves so I put a portable radio inside it and put the lid on.
    The radio continued to play so who knows. I guess the can was resonant to the frequency of radio station. I had the cardboard cut so that the galvanized metal top touched the galvanized metal can when the top was on.

    I’m wondering about some sort of combination container. For example a non conductive box with a fine wire screen around it with the wire screen covered with a non conductor and all of that inside a solid metal container.

    You just never know what an energy source will decide to do or where it will go. For example, my house was hit by lighting many years ago.
    At the time of the strike there was a window A/C, a TV set and a refrigerator plugged in and running. They were not hurt but the lightning strike blew the main breakers out of the breaker box taking the box cover door off with them. Every light bulb in the wall circuit that the TV was plugged into was blown even though none of them were switched on and the TV was on but was not hurt. All of the outdoor flood lights and driveway lights were destroyed. I mean lights and wiring were destroyed but none of them were switched on. It’s clear from that the lightning didn’t follow the easiest path to ground.
    It also didn’t hurt the water pump or the water heater or furnace. All of them were tied to the common house ground.

    I know that lightning isn’t RF or an EMP but it is a huge energy source and I predict EMP will be just as unpredictable. The long and short of it is do the best you can. Build more than one type of faraday cage. Place them in different locations and split your gear between them. Then hope for the best.

    • Rob Crawford says:

      The radio still picked up the station because the signal was still penetrating the can. That doesn’t mean it won’t work against an EMP; the radio is MEANT to find a weak signal and turn it into something you can listen to.

      EMP damages by inducing too high a voltage in circuits not meant to receive such a signal. Cutting the strength of the EMP sufficiently will protect your electronics, and you’re unlikely to build a full-spectrum fully-isolated chamber on anything less than a major laboratory’s budget.

  8. Arthur,
    As a EE I think that this article was spot on; although perhaps a little more complex in the description of the physics than it would have to be . Good job.

  9. Chuck Findlay says:

    The first thing is that I don’t see an EMP strike as a very likely event. But with that said I do apply a little protection to this very small possibility.

    My faraday cage is an old white metal cabinet I tore out of a house I was updating. It looks to be made in the 1960s and is as strong as the day it was made. It’s just dated in it’s style. It resides in my basement and the electronic items in it don’t seem to care if it looks dated. And the price was right, it was free. In fact I got paid to remove it and haul it away.

    And it’s easy to put things into and take them out of it.

  10. I dont think you all got my point, You have explained what an EMP does and how long it lasts, but you, me and everyone here does NOT know when one will happen. THAT is my point WE dont know when one will happen. So keeping your electronics stored in a Faraday container does no good if you have the irrational fear that a EMP/Solar burst will happen. I must point out that even if your cell phone works cuz you protected it in your faraday box the cell towers/internet wont be working. So whew you have a cute little paperweight that can make a phone call to no one else. I want to think I can get around when TSHTF happens without the dependence of a cellular device,Who are you going to call? 911 we are knocked out as well. I dont store my fire engines in an encapsulated faraday fire dept.

    • you could keep a laptop you dont use with alot of pdf files . sim cards, flashdrives, if it large enough a small tv,dvd combo , 2 way radios, ect…

    • charlie (NC) says:

      What you keep in your Faraday cage always are the spare electronic parts for your car or truck, your spare ham radio, your extra laptop computer, etc. etc. Then you put your everyday items in the Faraday cage when you aren’t using them for a while. Otherwise you use them and don’t worry about it because you have your spares put away. It’s not that complicated.

      The amount of stuff you keep stored away depends on your risk tolerance. Some folks don’t have insurance. Some folks have too much insurance. It’s the same thing. It’s just insurance in the form of electronic items.

      • Jersey Drifter says:

        well stated Charlie.
        If you have a set of 2 way radios that work ok in your area, and you are happy with them, then buy a second set and put them in the cage.
        One is none, two is one.
        A back up plan for your back up plan.

    • I keep hand held wallis talkies for communication on the farm and with my neighbors Ina faraday box. I also plan to put a watch and a compass in there. A working computer with my saved documents would also be nice.

    • Rob Crawford says:

      Protect your spare/emergency gear. Yes, your cell phone may get fried — but, as you said, the rest of the network may get fried, too.

  11. Chuck Findlay says:

    Hey MD that “Bad Idea” t-shirt add is very distracting.
    I think you need more like it…

  12. Millie in KY says:

    Sooo….we hear about the event and hustle to put our electronics away? I guess I’m confused, if a small nuclear device is set off in the upper atmosphere with the intention of doing harm to our electronics, we probably would have no warning. We would keep our stuff in there all the time? That doesn’t make any sense to me at all….someone please explain why this is important, as someone said, if my stuff is put away, how do I use it? Thanks!

    • The whole point is to stuff up a few spare electronics in your cage. A CB radio, flashlights, AM/FM radio (just in case…), electronic tools of value, etc.

      Not only comm equipment. A glucometer, for example, is almost vital to a diabetic person. And it could fry in an EMP. Better have a spare one stashed somewhere safe =P

      You do not use your stuff. Your everyday gear will fry. That’s it, there’s nothing you can do about it. It’s your preps you need to store =)

  13. Ben Price says:

    In a word, bogus, all of it. Neither the author nor anyone replying has any idea how a faraday cage really works. But if y’all want to put your electronics in trash cans and expect them to survive an emp, at least you will be one step ahead of the rest when they pop. A trash can will be a good place to leave them after they are fried.

    A faraday cage must have a good earth ground. It should be constructed of perforated metal, preferably copper. It should have no open seams, and the contents need to be electrically isolated from the cage if they are to be protected.

    The reason for the earth ground is that the cage IS NOT A SHIELD, it is a shunt. It will not deflect EMP energy, it has to drain the energy instantly from the surface of the cage before it builds up a charge and becomes electrically transparent. The perforations are necessary to break up eddy currents in the metal, otherwise it will induce a saturating field that will re-radiate into the cage.

    But go ahead and use the garbage cans, the ammo cans, the aluminum foil packets, the coffee cans, etc. and see what happens.

    From one with REAL experience building, testing, and using faraday cages for a living.

    • Ben,you may be right but your presentation leaves a lot to be desired. just sayin.

    • charlie (NC) says:

      Ben, I don’t particularly like your attitude but I’ll reply anyway.
      Lots of people know how a Faraday cage works. What we don’t know is the characteristics of the EMP event. Without that information we are guessing on what to protect against.

    • Macintosh says:

      It’s good that you do such important work with things for a living because if you had to interact with people you would be out of a job.

    • I think that you’re confusing the characteristics of an EMP with that of lightning. The goal with lightning is indeed to shunt it away (thus the use of lightning rods). An EMP is a high frequency radiated event (not conducted like a bolt of lightning), so the goal is to simply shield the sensitive electronics from the high electromagnetic fields. I am not sure of your experience, but I say this as a NARTE certified EMC engineer who has worked in electromagnetics for 20 years.

      As for garbage cans, they do a pretty good job as I show in my book.

      Best wishes,


    • can a dryer be used as a Faraday cage

    • As somebody else in the radio field, I am going to have chime in to state that your information is not correct, either here or your improved explanation below. A ground provides a safe place to direct excess current from lightning strikes, power line surges or static discharge to protect your more delicate electronics. EMP is a high energy radio wave, but radio waves are not current flow, otherwise they couldn’t go through air which is an insulator.

    • Djimnik says:

      He’s right, but it really doesn’t matter. A high altitude nuke EMP will generate upwards of 25,000 volts per meter within a close distance and 5000 volts per meter out to around 1500 miles from zero. Anything with a wire more than 3 feet long is going to be fried. Every single car in the nation will not be running after that. Also an EMP is not a radio wave, it’s a magnetic field. Any time a magnetic field moves across a conductor it generates voltage.

      • Djimnik says:

        Some articles I’ve read refer to super EMP devices, nuclear devices designed for maximum magnetic yield. Some where around 200,000 volts per meter of wire at zero and 100,000 volts at the horizon. Who knows if they are real, all highly classified.

  14. Chuck Findlay says:

    I use my stuff as normal. But I work hard to have backups of almost everything. These things have to be stored someplace, why not the metal cabinet I got for free. Its convent as it has shelves in it and it is made from metal.

    Like I said, I don’t worry about EMP, but it’s easy to put things in this cabinet. I don’t expect to have a serious auto accident, but that doesn’t mean I don’t buy coverage for it. I look at EMP the same way, I cover my bets.

  15. I’ll take a chance with my old microwave I have. It’s tidier than lining a closet with tin foil, which looks like I’m doing something illegal, and it lets me avoid hauling the old clunker out to the curb. I only have a couple walkie-talkies, a transistor radio and a couple flashlights in it, with no batteries in them.

    If it does happen, I figure it at least gives me a fighting chance, and if I do have a break-in, chances are that the burglars will overlook that antique. I did snip the cord in preparation to junk it, but managed to procrastinate tossing it. I’m glad I did now.

    • And that microwave of yours already is some kind of Faraday cage, by the way.

      It was designed this way =P Not to let the… micro-waves out of the oven.

  16. – it echos, and expands upon, the advice of the OP, and it’s free.

    No shield is 100% protective. Every electronic device will have a different failure threshold. The pulse strength will vary based on it’s height, your distance from it, and the magnitude of the blast. Cages attenuate the strength of the pulse the item within receives, they don’t fully negate it. The skin effect is fact, multiple thin shields, each insulted from each other, is far superior to a single thicker shield like a trash can. Conductor, insulator, conductor, insulator, etc, device. Read: electronic item(s) in a paper bag, wrapped in tinfoil, inside another paper bag, wrapped by tinfoil, inside another paper bag, wrapped in tinfoil. Improper grounds are worse than none at all. A copper wire to a grounding rod, or a water pipe, is not a proper ground for EMP.

    • You’re absolutely right about the multiple layer effects working better than a thick conductor. I didn’t have time to talk about that in this article, but it is discussed in a youtube video that I did. Check out disasterprepper videos (or my name) and you’ll find one on Faraday Cage testing.


  17. I have a lead lined ammo box , that was originally used to transport radioactive pharmaceuticals in for small stuff .

  18. Ben Price says:

    Yes, my delivery does leave something to be desired. My apologies to the pack. I get irritated having to repeat myself often regarding all the mis-information going on with phony/inadequate faraday cage specifications.

    An EMP is an induced pulse of electromagnetic/electrostatic energy ranging from very low frequency (heave) to extremely high frequency (Compton effect). There are several components to the nuclear detonation type emp that have to be considered. Also, the altitude of the detonation is a factor in electrostatic/electromagnetic generation. The theory behind nuclear emp gets rather complicated to explain, so I would offer a rather simplified analogy.

    Instead of thinking of a faraday cage like you would an umbrella in a rainstorm, think of it instead like a sponge you are standing under. If the storm is small and short, the sponge will absorb enough moisture that you don’t get soaked. But if the storm is heavy and/or long, the sponge will saturate, and you will end up as wet as if you had no sponge at all to protect you. Now imagine if the sponge had 4 pipes sticking out of the corners, stuck in the sponge so that they could drain the sponge before it saturates. Then you could stand under it during a heavy storm and still stay dry. However, under the worst storm conditions, even the pipes would not be enough, and you would end up soaking wet after all.

    That is perhaps the best analogy I can come up with for how a faraday cage is supposed to work. The pipes are the same as the grounding rods. If the rods are not coupled to both the cage and earth ground well, then they will not shunt the energy sufficiently to protect what is inside. If the emp is big enough, it will overcome the abilities of the cage. I have never seen or heard of a faraday cage that will protect against ANY emp. But unless it is well grounded, it won’t provide any protection at all.

    If you want to understand emp better, visit the site www., or do a google search on nuclear emp. Also do search on “mitigating emp” and do a lot of reading.

    I’ve had to harden communications sites, some of the most vulnerable equipment to emp, to survive direct lightning strikes. Lightning is freakishly difficult to protect against electrically. But it is not as bad as nuclear emp can be.

    My apologies if I seem curt or irritated. It is because I have repeated this so many times I wonder if anyone is listening.

    • charlie (NC) says:

      Ben, finally a useful comment from you. Thanks and I mean that sincerely. This groups includes folks from all different
      backgrounds, levels of experience and education so please don’t make the assumption that all or even most of us are too ignorant to understand you. As I told my doctor once. I understand the English language if you can speak it.

      I don’t mean those comments to be harsh. I guess you can tell that you are not the only member of this group with a hopelessly abrasive tongue. Your analogy with the sponge and the pipes is the best word picture I’ve ever read/seen of an effective faraday cage.

      Am I right in thinking that probably the very best protection for
      an EMP is to bury your stuff under about 5 or 6 feet of soil?

      • Ben Price says:

        Deeper would be better, but keep in mind depth is a bit subjective. What you really need is a good coupling to earth ground. That depends more on soil conductivity and things like ambient moisture, mineralization, as well as depth. Dissipating the energy over a broad area quickly is the objective. EMPs are neutralized quite well in the ocean.

        I am a bit of a curmudgeon at times. Usually I don’t have such an abrasive tone on my responses. I guess the stress at work has been getting to me a bit lately. Again, my apologies.

    • william Kraft says:

      Just curious, if you need an earth ground how far away from your cage would you place it.

      • Rob Crawford says:

        As close as possible, by his model. You want do dump the energy ASAP, longer lines introduce delays and resistance to the energy moving away.

  19. Thomas T. Tinker says:

    Well Crappolla boys and girls, don’t you love the constructive interaction. Somebody with a plan kindly write it up with some art work attached. Hell everybody with a plan do a write up and we can all hope to find something that will protect our spare am radio and IPod!

    Me….. I believe I’ll just attach a ‘defferent’ style of lid, a kind of seat really, and use mine as a standby crapper.

    Tell be Packers….. what is the effect of a nice juicy EMP on brass cased ammunition and mylar bagged pasta?

  20. I’ve read so many articles, and Dr. Bradley’s books (very intelligent on the prepper front!), and there is a ton of information on the web and in books about EMP’s (both solar and nuclear) and it can get confusing.
    Some say that anything that can be disrupted by a magnet can be wiped clean of all information, short circuited, etc. So flash drives, CD’s, DVD’s, computers, etc can all be wiped clean and also rendered unusable.
    Having a backup of all of your information in a safe place….not on some distant server because it will definitely be wiped clean… a faraday cage would be the best route to use. IF you can afford it, buy a backup of all electronic equipment…..laptops, walkie talkies, emergency radio, ham radio, etc. Not sure about battery operated stuff like flashlights, especially ones with batteries in them, but they would probably be best kept in a faraday cage as well. I’ve got so much backed up on various types of discs and flash drives that I’ve lost track of all of the info and pictures and music I’ve got. But I do have a laptop that I don’t use except during storms, so I plan on putting it into a faraday cage of some design. A metal trash can would be best as it can be used for trash after the EMP is over. I’m going to put a rubber mat on the floor, plus the inside of the lid, and up the sides to add to the protection, as well as running a copper wire into the ground from the handles so the extra energy will be shunted off into the ground. At the moment, I live in the basement of an 1895 house that has a hand laid brick floor without mortar, so putting a copper wire into the floor would not be a hard thing to do.
    If you can find the Apocalypse 101 shows that were on National Geographic, (look on the National Geographic site or YouTube) the guys actually made a faraday cage, and it seemed to work pretty well. They used a rubber floor mat on the bottom of the cage, and shunted the energy off into the ground from the cage with a copper wire and a metal pole of some sort.
    I’m not a huge fan of surge protectors because my computer has been fried TWICE being plugged into them. So I’m not a big advocate of the surge protection devices. During a severe thunderstorm….my computer gets shut off and the surge protector unplugged from the wall. Earlier this year it was unplugged for almost a month for all of the severe storms rolling through here. Didn’t make much sense to plug it back in when I was just going to have to unplug it a day later.

    • The TN Man says:


      This isn’t meant to be critical in any way… It’s just my attempt to make the point that some forms of data storage are different that others. ALL forms of storage have their drawbacks.

      CD and DVD disks aren’t affected by magnetic fields, but are temperature sensitive. Think about a CD left on the dashboard of a hot car.

      You are correct concerning magnetic data storage, except for the CDs and DVDs. They are both “optical” storage devices which still digitally store the data, but instead of magnetized spots (the spot being magnetized or not representing the binary ones and zeros) optical devices store data with “shiny spots” or “not shiny spots”. The spot either reflects the “laser/light” or it doesn’t reflect it.

      The physical size of the disk and the size of the beam of light used determine how much data can be stored on the “media” CD (about 700 Megabytes) or DVD (about 4 gigabytes).

      I’ve been dealing with computer hardware since the time of “Low Density” 5 and a 1/4 inch 180 Kilobyte floppy disks (early 80’s).

      The shielding provided by a Faraday Cage is entirely dependent upon the FREQUENCY (and therefore the WAVELENGTH) of the incident waves.

      • Ever put a CD/DVD in a microwave? (I don’t recommend it, watch a youtube video first.)

        But this is an excellent way to destroy all data on it. I suspect an EMP would have the same effect.

  21. PrepperNurse says:

    this is my first visit to the site. I agree with many comments, but I believe we should all respect each other in a professional manner. For an EMP….which could have happened 2 weeks ago with the Earth that just dodged a large solar flare, I keep spare items in an old insulated Colman cooler from the 1960s….the metal outside and insulated inside. I read somewhere that this would do well for the box and you can find the cooler relatively cheep at garage sales and auction houses. Just need to clean it and if so desired, throw a coat of spray paint on it. A metal tool box will work as well but make sure you line it with Styrofoam to place your item(s) on. I do like the idea of grounding… will consult with my father who was a mechanical and electrical engineer before he retired.

    Thank you all for stuff to think about.

  22. mitten mom says:

    Newbie here, so I apologize if this has been addressed before or if it is so basic that it is a “given”. Would galvanized sheet metal, the same type that is used for ductwork for HVAC, be appropriate? My husband is in the HVAC industry and that is something we have at our disposal. I realize that insulation of some type would be needed, along with the other specs that are required. I have searched for info on this but haven’t been able to come up with this answer. Thanks to all of you for making this site so worthwhile!!

  23. Mitten Mom says:

    Newbie here, so I apologize if this has been addressed before or if it is so basic that it is a “given”. Would galvanized sheet metal, the same type that is used for ductwork for HVAC be appropriate? My husband is in the HVAC industry and that is something we have at our disposal. I realize that insulation of some type would be needed, along with the other specs that are required. I have searched for info on this but haven’t been able to come up with the answer. Thanks to all of you for making this site so worthwhile.

  24. Hi
    great info
    would a Faraday cage help people that have electrosensitivity to be able to use computers ?
    maybe put the computer in the cage or make the cage big enough for the ElectroSensitive person to get in so they can use a computer ?
    any thoughts or ideas ??

  25. Thank you for the instructions! Very informative. I was wondering if you could also show designs for some kind of Faraday hat? I think it would be helpful to a lot of readers (myself included).

    • userError says:

      I think there were instructions in the comments… paper bag wrapped in foil, layered as needed. I approve of this approach as it also improves my looks.

  26. Okay so I understand the need for a Faraday cage and everything, but what is the point of having all of that stuff when it can’t really be used very long without a power source to recharge it? Let’s say a solar flare fries the electrical grid and you managed to save your laptop from the damage…You can only use it until the battery dies and then it is useless again. So unless you build a Faraday Cage to go around a generator or something that allows you to recharge it (and you don’t get killed from the attraction of everyone realizing you have a power source still) everything will eventually become useless. As for a radio who are you listening for over it without anyone having the ability to broadcast? I guess my point is… isn’t it pointless to save any of that without some way to power them again long term?

  27. If I built my trash can Faraday cage, put my cell phone in there with the lid on tight, and it could still receive a text message, is it safe to say my cage is worthless against a powerful EMP?

  28. MD,
    I would suggest that when reprinting a previous article, you should state that in the opening. After reading the June 2, 2014 article from Dr. Bradley on EMP that mentioned a followup article on Faraday cages, I was not surprised to see the article; but, was surprised to see my comments.

  29. Old Hillbilly says:

    Unless I have just missed it ( a good possibility with these old tired eyes), I have not seen any discussion of LARGE Faraday cages. I am speaking here of a Conex box, or ocean freight shipping container. We have a 40′ box set up as a Faraday cage, or at least that is the intent. It is sitting in the woods on wooden timbers. It is all metal except for the floor which is plywood. We have covered the floor with 4′ x 8′ sheet metal panels (the type used to make HVAC duct). It is not yet grounded but soon will be. The plan is to use our tackhoe to bury an old motor block deep in the ground and attach it by heavy metal cable to the frame of the box. Now…here is my question which regards testing of the box. I have read often that to test the effective of a Faraday cage one should put a cellphone or small radio inside and see if you can hear it ring or hear the radio broadcasting. If not, then you have a good “seal” but if the device works, you have a “leak”. When we got our Conex set up and the floor lined with metal, one of our guys got inside with his cellphone and we closed and locked the container door with him in there. He then dialed his home phone and his answering machine picked up. Does this mean the box is NOT effective as a Faraday cage or is our testing method flawed. It is not yet grounded but once we get the ground in will it prevent a call from being made? The doors on a Conex have a gasket seal. Could the signal be leaking around the seal? Could the individual holding the cellphone be acting as his own antenna giving the phone signal more strength to go through the walls of the box? Is this a viable test?

    I know I have presented a lot of questions but we have quite a bit of money invested in this project and just want to set it up so it will work. Any and all thoughts from the OP or anyone else would be appreciated. This container will be used to house “spares”….generators, radios, ignition components, spare chainsaws, you name it.

    Thanks for any assistance.

    • Old Hillbilly,
      This is one of those proving something that can’t be completely proven. If a radio or cell phone works inside the box, then there are RF paths (leaks) into and out of the container; however, if radios, cell phones, etc. do not work, it doesn’t guarantee that the box will work in a real EMP event, but gives you a much better chance. Also, storing items in smaller Faraday Enclosures, like wrapping boxes and other containers in continuous layers of aluminum foil will add that one additional protective layer.

      Grounding the box will most likely not provide any additional protection. Leaks can come from the gaps in the door (overlapping metal mesh can help there, or can be tiny gaps in the metal you used on the floor. Years ago I was working with some other engineers trying to find an RF leak in a Faraday room we used for testing. The room was built completely of extremely fine copper mesh and copper foil. It turned out that there was a small spot where the copper foil layers hadn’t been completely soldered, and a small piece of silver solder and a heat gun finally corrected the problem, after nearly three days of looking for it. In this case, grounding the enclosure made the signal (incoming to a spectrum analyzer) go away; but, that was because the ground gave the signal a path with less impedance (RF resistance) than going through the gap in the foil, so in this case a ground actually would have hidden the real problem.

      In any case, the Conex container will give you better protection than having things just sit out in the open since it will help reflect and shield things inside from the impinging RF radiation.

  30. Nancy V. says:


    I appreciate your article. Building faraday cages out of available materials now sounds less intimidating that I thought.

    I do have a old family 1950 ice chest I keep radios in, and didn’t realize the gap could cause potential exposure. I will go back and read older posts about EMP and educate myself better.

    Here’s my question: If I wanted to test the ice chest’s EMP protection value, how would I do it?

    I can measure small values with my TriField 100XE

    Any advice anyone has on this would be appreciated.

  31. Your ability to receive a cell signal is dependent on the distance from the cell site and the shielding of your Conex. As it is impractical for you know how far you are from the nearest cell site, this is not a recommended method for testing the effectiveness of the shielding. I would recommend using an AM/FM radio and verifying that you can’t pick any stations on either band instead. That said, if you are able to pick up a cell phone signal, it does indicate the Conex is not nearly as effective Faraday cage as I would have expected a welded steel container like this to be.

    I suggest using the cell phone and while walking from the front to the back, see what the signal bars are showing for signal strength. If you have fewer bars at the back than by the door, this would indicate the doors are the weak point. If it is the same throughout, then it may be the floor or some other spot where it is getting in. An AM radio will also work as you will hear more static as the signal strength goes down. An AM/FM radio that has a signal strength meter would also work.

    The best Faraday cage would be a box that had been welded shut with no holes. Needless to say, this isn’t a practical Faraday cage as there would be no way to access the contents. As such practical ones are designed such that the door makes a continuous electrical contact with the body by having exposed metal at the contact point between the two. As such your gasket may be your weak point. That said, removing it may not work either as doors probably wouldn’t fully close without it there. I suspect you may be able to a improve the situation by running ground wires between the doors and the body of the Conex. You also want to look at minimizing the metal to metal distance between the doors and the body. I would also inspect the structural integrity of the Conex to verify that it is one solid box.

    You do not become part of a cell phone antenna when you are holding a cell phone. As such the person holding the cell phone did not increase the signal strength of the cell phone. The engine block is an interesting idea, but I would have stuck with standard ground rods. Remember that the point of grounding is minimal electrical resistance to the dirt, so you want heavy wires, direct metal to metal contact and maximum surface area in the dirt, which would be easier to achieve with standard equipment. Also, grounding will help protect against lightning strikes, but will not have much of an effect on EMP, either helping or hurting.

  32. All well and good, as long as you have enough advanced warning of the EMP event to put your stuff into the Faraday Cage!! I don’t see alot of advance warning as likely happening.

  33. Chuck Findlay says:

    Hey MD a question, why did my post of 11-months(July 2013) ago get posted here now (June 2014)?

  34. Douglas says:

    If I was to use welded steel, would that work for a room?

    • Douglas,
      Yes. You’ll note in the article that just about any conducting metal will work OK. The main thing is no gaps between the welds, and a good connection, usually using braid (think steel or copper wool) in any gaps like a door. The thing is to get any gaps smaller then the a few millimeters.

  35. Chucker says:

    Wow! Very interesting comments and ideas. I was considering a steel building with insulator’s attached to the inside and attaching a metal screen to the insulator’s. I haven’t quite figured out if I should ground them separately or in parallel. I was also considering adding large capacitors to the outside frame to help absorb and dissipate the energy in which I would ground them sepeately. Any ideas on this idea?

    • Chucker,
      If you’re using a steel building, then the insulators and metal screen wouldn’t be required, unless you’re simply using the screen to construct a Faraday enclosure within the building, in which case the material of the building would not matter. Grounding is not required, and I’m not sure what use the capacitors would b in this situation, since the point of grounding (if you do so) is to drain the energy as quickly as possible, something the caps could inhibit.

      • The TN Man says:


        Capacitors “allow” Alternating Current (think house hold power AC) to flow but block Direct Current (think of a battery) to flow/discharge to ground. A capacitor would charge up and “hold the charge” for a longer period of time (depending upon the size/capacitance of said capacitor).

        In working with sensitive Electronic components (the same thing we’re trying to protect from EMP, technicians refer damaging/protecting from damage by ESD (Electrostatic Discharge) we use “grounding straps” that have Resistors to allow both AC and DC currents to flow while restricting the current flow (amperage) to some relatively low level. The preferred size of the resistor depends upon several factors, but typically should be in the 1 to 10 Megohm range. The “grounding strap” is worn on the wrist or ankle of the worker with the other end connected to “Ground”.

        In operating electronic equipment “grounding” of the “shield” of SOME conductors will have a capacitor installed to “Shunt or discharge” AC to ground while blocking the DC. Size is typically quite small in the “Micro Farad” range.

        Hope this helps. Effective grounding of electrical/electronic equipment can take up a whole chapter in a textbook if you want to get into the theory and explanations of how to calculate it. I’m not a EE (Electrical Engineer) just a retired Navy (US) Electronics Technician.

        • Chucker says:

          Thanks for the great feed back. I will find another use for my caps, maybe to boost my solar capacity.
          Ya’ll have a great day; ’cause if YOU don’t do it, it won’t get done! And thank you for your service!!

  36. Hunker-Down says:

    Thanks Mr. Bradley and everyone for a lively discussion.

    My takeaway from all the viewpoints is, “it depends”. Engineering is way above my mental pay grade, I wouldn’t know an ohm from a lug nut.

    To those who find it impractical to store, retrieve and again store items, it seems to me that backup items should spend their days in a faraday cage and everyday use items should have a backup. You do have backups, don’t you?
    We use an old metal picnic cooler for our radio and scanner. We cant afford backup devices, and are still accumulating basic communication devices.

    We all have seen electronic storage devices become useless because the device readers become obsolete then discarded. Floppys with no floppy reader are coffee cup coasters. The reference material I want to use after TSHTF is a printed sheet of paper (several thousands). EMP safe.

  37. I’ve been using an old metal file cabinet as my faraday cage. Is that acceptable? Been thinking of making another one as well, but not sure what materials I’ll use.

  38. rjarena says:

    Am I asking the obvious, what about a gun safe?

    • The TN Man says:


      The safe should work to an extent, but would be better if the door has a hard “metal to metal” contact, or the “opening” was taped over with metal/conductive tape.

      Without the tape or proper seal your safe would be in the same grouping as “Rick’s” old microwave, “Old Hillbillies” CONEX box, or “Chuck Findlays” free metal cabinet.

      Most anything would be better than nothing but it is all really DEPENDING upon the magnitude of the EMP and it’s frequency (wavelength).

  39. I am curious about your first post. One of the things you mentioned as working post EMP would be generators. Were you referring to the large industrial size or the homeowner size or both. I have a small generator to pump my well and am concerned about what parts would be fried. I looked at an on line parts site and the cost of the parts would be astronomical. cheaper to buy a spare generator. Reminded me of being in back in the 70s and looking at the parts dealers part book, Over $17,000 to build a $1900 bike. Which parts would I have to worry about? It runs on propane and is not plugged into the grid.

  40. Buckwheat says:

    Thank you for all of the wonderful information. I have a couple of questions:
    1) I have equipment such as a generator and solar panels that do not fit in my (trash can) faraday cages. I have been thinking that I can convert an enclosed 5×8 or 6×10 trailer to a faraday cage with a few mods. Do you see any problems with this logic? Have you seen other items used besides microwaves and trashcans?
    2) I am really interested in keeping a duplicate car parts in a faraday cage but can never get a straight answer on the items I must keep in a faraday cage. I have been told to buy a computer and ignition switch – is there anything else?
    3) I have read in a couple of survival themed books (most recent by An American) where they have used copper mesh to encapsulate the safe room and it protected the HAM and other gear. Can you expand on what it is and where to get it?
    Thank you very much!

  41. I bought a solar humless generator w 100 watt solar panels for charging it. It was shipped in a heavy cardboard box w heavy copper staples and 1/2inch styrofoam pieces as package materials. Can I use the cardboard box it came in as a faraday box if wrap the outside with several layers of heavy duty foil and do the inside also? Are the copper/copper colored staples a concern and does it make a difference what side if the foil, shinney or dull, faces towards the inside of the box? The generator is also inside a heavy thickness plastic clear bag. Do I leave the bag on and wrap it in foil as extra precaution? What/how do you suggest prepping my generator from what I have told you? I have not taken the solar panels out of their box yet but will faraday them also. These will be my creature comforts wtshtf. Your input appreciated as I have to get this right the first time without error. Thank you and regards.

  42. I’ll take my chances with my old microwave oven/anti-static bag setup. I only keep a pair of FRS/GMRS radios in there, batteries removed, a couple of LED lights (they have an IC circuit inside), and a flash drive with my important stuff on it. Based on some of the comments, I may make some tin foil bags to bolster the protection, or maybe get a small ammo can if I can find one to fit. I don’t use those items daily-daily, so it doesn’t matter it I do slap some tape around the door seam. As a matter of fact, I’ve got part of a roll of it gathering dust, and I think I’ll do that now.

  43. Would an EMP affect solar panels?

  44. Kathleen says:

    I’m about to turn a closet into a faraday cage and am planning to put down a layer of heavy duty aluminum, then a layer of aluminum screen, followed by a layer of plastic, with probably a wooden floor. I am wondering if I can attach the aluminum, screen, and plastic with standard staples or should I use something else like liquid nails?

  45. I think this is a very good idea to build a Faraday cage for a safe room in my house since it has possible health benefits.

    • I’m no doctor but I’m pretty sure that a Faraday cage doesn’t provide any health benefits. Having said that, it is possible that a Faraday cage will stop you from getting killed by lightning. Not getting killed by lightning is always very beneficial I guess, from a health perspective.

  46. I have two questions. First how does the chicken wire in old plaster fit into the Faraday Effect. I assume that the gaps are to large to be of much use, but was curious about it. The other question is would a metal building, like our workshop provide such protection?


  47. How can I provide shielding for big equipments from external Electrical noises, mainly caused by arcing of surrounding equipments?

  48. Someone mentioned that EMP effects are mitigated in the ocean. Could I take a large water filled container say a plastic 55 gallon drum or a swimming pool and submerge a electrically insulated, watertight container with the items I want to protect? Providing of course that the watertight container did not come into physical contact with the bottom of the pool. Thankyou in advance.

  49. When using a garbage can and lid as a faraday cage, does the can need to be grounded to absorb the effects of an EMP? Does it make any difference if the can is resting on dirt versus some sort of asphalt or concrete?

  50. i have a diesel car. what electronics would i have to have in the cage, just the cpu or would ALL the electronics of the car be zapped? starter ignition etc

  51. CAUTION! Why should we imagine an EMP as a one-wave event? Consider: A terrorist bombs a market. Ten minutes later, first responders arrive to rescue the victims. Then another bomb detonates. An EMP attack might expand on this heinous plot. The intent to demolish backup electronics will cause our enemy to launch second and third EMPs. Unthinkable? No! Expect *multiple* attacks!

  52. Quick question…I. Building a faraday cage inside a 40 foot sea container. I”ve framed the container and put up ply board. The interior is going to be 3mm aluminum sheet metal. Is having the the faraday cage bolted to the interior of the plyboard going to work or lose effect? Should I tear down the frame and interior and just bolt the aluminum directly to the steel wall? My floors are also wood, how ever Im Covering them With Aluminum sheet as well. So basically can my exterior be wood and interior be metal?

  53. Im constructing a faraday cage inside a shipping container, my walls are wood, should I bolt my metal sheet to the interior of the wooden frame, or is it best to bolt metal sheets directly to the steel wall and floor it self…basically my question is will a faraday cage have effect with a wood exterior and a metal interior?


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